1. Field of the Invention
The present invention relates to the field of footwear. The invention concerns, more particularly, a flexible shank for an article of footwear that provides support to the bottom of a user's foot along with flexibility in one or more selected directions.
2. Description of Background Art
Conventional articles of footwear include two primary elements, an upper and a sole structure. The upper provides a covering for the foot that securely receives and positions the foot with respect to the sole structure. The sole structure is secured to a lower portion of the upper and is generally positioned between the foot and the ground. In addition to attenuating ground reaction forces, the sole structure may provide traction, control potentially harmful foot motion, and support the bottom of the foot and the arch. Accordingly, the upper and the sole structure operate cooperatively to provide a comfortable structure that is suited for a wide variety of ambulatory activities, such as walking and running.
The upper forms a void on the interior of the footwear for receiving the foot. The void has the general shape of the foot, and access to the void is provided by an ankle opening. Accordingly, the upper extends over the instep and toe areas of the foot, along the medial and lateral sides of the foot, and around the heel area of the foot. A lacing system is often incorporated into the upper to selectively increase the size of the ankle opening and permit the wearer to modify certain dimensions of the upper, particularly girth, to accommodate feet with varying proportions. In addition, the upper may include a tongue that extends under the lacing system to enhance the comfort of the footwear, and the upper may include a heel counter to limit movement of the heel.
The sole structure of conventional articles of footwear generally incorporates multiple layers that are conventionally referred to as an insole, a midsole, and an outsole. The insole is a thin, comfort-enhancing member located within the upper and adjacent the plantar (lower) surface of the foot to enhance footwear comfort. The midsole, which is traditionally attached to the upper along the entire length of the upper, forms the middle layer of the sole structure and serves a variety of purposes that include controlling foot motions and attenuating ground reaction forces. The outsole forms the ground-contacting element of footwear and is usually fashioned from a durable, wear-resistant material that includes texturing to improve traction.
The primary element of a conventional midsole is a resilient, polymer foam material, such as polyurethane or ethylvinylacetate, that extends throughout the length of the footwear. The properties of the polymer foam material in the midsole are primarily dependent upon factors that include the dimensional configuration of the midsole and the specific characteristics of the material selected for the polymer foam, including the density of the polymer foam material. By varying these factors throughout the midsole, the relative stiffness, degree of ground reaction force attenuation, and energy absorption properties may be altered to meet the specific demands of the activity for which the footwear is intended to be used. In addition to polymer foam materials, conventional midsoles may include, for example, stability devices that resist over-pronation and moderators that distribute ground reaction forces. They may also include support features in the arch region, or they may include a removable arch support placed on top of the midsole.
Some conventional articles of footwear for use with dancing and dance-related activities, such jazz shoes, dance shoes, and dance sneakers designed for use with exercise routines, have extremely flexible sole structures. These sole structures provide little support to the foot, and often lack a midsole entirely. These shoes permit the user to easily flex the arch region of the foot for various dance steps, but lack support for the user's arch. Other types of dance-related shoes have stiffer sole elements that are desirable for various movements such as turns and toe stands, which may include an arch support, but that are difficult to bend in the arch region.